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| United States Patent |
6,110,625
|
|
Wen
, et al.
|
August 29, 2000
|
Methods for manufacturing color filters
Abstract
The invention relates to a method for manufacturing color filters utilizing
a color electrodeposition coating which contains an anionic
electrodeposition resin having a low acid value. Said method comprises
coating a layer of positive photoresist onto a transparent electrically
conductive substrate, exposing the substrate under a photomask or
photomasks to form regions of different initial levels of exposure energy,
exposing the entire surface of the substrate through an
energy-incrementing way to, progressively, allow all regions of the
substrate to achieve an energy sufficient to completely expose the
photoresist on each corresponding region, developing stepwise each region
with a same developer solution to cause the electrically conductive
substrate of the corresponding region uncovered, electrodepositing said
region with a color electrodeposition coating containing an anionic
electrodeposition resin having a low acid value to finish the pixel
arrangements of the desired colors and completely exposing the substrate.
The low acid value anionic electrodeposition resin utilized in the
invention has an acid value of 1 to 70 mg KOH/g. The method of the
invention shows the advantages of having a high degree of freedom in
pattern figures and a wide process window. Moreover, the manufacture color
filters of large surface and the perfect yield rate of products are
possible.
| Inventors:
|
Wen; Chun-Hsiang (Hsinchu, TW);
Cheng; Shu-Huei (Hsinchu, TW);
Cheng; Hua-Chi (Hsinchu, TW);
Wu; Yaw-Ting (Ping-Chen, TW);
Jan; Ming-Shiang (Chutung, TW);
Hsieh; Pao-Ju (Keelung, TW);
Yasukawa; Jun-Ichi (Chigasaki, JP);
Kuwahara; Hajime (Narashino, JP)
|
| Assignee:
|
Industrial Technology Research Institute (Hsinchu, TW);
Sumitomo Chemical Company, Ltd. (Tokyo, JP)
|
| Appl. No.:
|
248375 |
| Filed:
|
February 10, 1999 |
| Current U.S. Class: |
430/7 |
| Intern'l Class: |
G02B 005/20; G02F 001/133.5 |
| Field of Search: |
430/7,321,394
|
References Cited
U.S. Patent Documents
| 5186801 | Feb., 1993 | Matsumura et al. | 204/181.
|
| 5478681 | Dec., 1995 | Yamasita et al. | 430/7.
|
| 5641595 | Jun., 1997 | Hsieh et al.
| |
| 5645970 | Jul., 1997 | Cheng et al.
| |
Primary Examiner: McPherson; John A.
Attorney, Agent or Firm: Alston & Bird LLP
Claims
What is claimed is:
1. A method for manufacturing color filters comprising the steps of:
(a) coating a layer of positive photoresist onto a transparent electrically
conductive substrate, and exposing the positive photoresist layer to form
three or four regions of different initial levels of exposure energy,
wherein the exposure energy of each region is D.sub.1, D.sub.2, D.sub.3
(and D.sub.4) progressively, D.sub.1 represents the full exposure energy
of the positive photoresist, and D.sub.1 >D.sub.2 >D.sub.3 (>D.sub.4);
(b) using a developer solution to develop and to remove the region of the
photoresist layer with the exposure energy of D.sub.1 to thereby cause a
corresponding area of the electrically conductive substrate underlying the
photoresist to be uncovered, and electrodepositing said region with a
color electrodeposition coating containing a low acid value anionic
electrodeposition resin having an acid value of lower than 70 mg KOH/g so
as to finish a pixel arrangement of a desired color;
(c) exposing the entire surface of the substrate with an energy IE.sub.n to
impart an incremental amount of energy to all regions of the substrate,
wherein IE.sub.n is the energetic difference between D.sub.n and D.sub.n+1
and the definition of n is below:
(i) when three regions of different initial levels of exposure energy are
formed on the substrate, n is 1 and 2 progressively, or
(ii) when four regions of different initial levels of exposure energy are
formed on the substrate, n is 1, 2 and 3 progressively;
(d) after each time of exposure in steps (c)(i) or (ii), using the same
developer solution of step (b) to develop and to remove the photoresist of
the region achieving full exposure to thereby cause the corresponding area
of the electrically conductive substrate of underlying the photoresist to
be uncovered, and then electrodeposition said region with a color
electrodeposition coating containing an anionic electrodeposition resin
having a low acid value to finish the pixel arrangements of other desired
colors;
(e) repeating steps (c) and (d) until all of the pixel arrangements are
accomplished; and
(f) forming an overcoat on the substrate.
2. A method for making color filters according to claim 1, wherein the low
acid value anionic electrodeposition resin is a polyester resin having
carboxyl groups.
3. A method for making color filters according to claim 1, wherein the low
acid value anionic electrodeposition resin has a acid value of from 20 to
70 mg KOH/g.
4. A method for making color filters according to claim 1, wherein the
anionic electrodeposition resin further comprises a crosslinkable curing
agent, an organic solvent, a neutralization agent or a coloring agent
consisting of a dye, a pigment, or a mixture thereof.
5. A method for making color filters according to claim 4, wherein the
crosslinkable curing agents is selected from the group consisting of
methylation melamine resin, butylation melamine resin, methylation
methanol melamine resin, butylation methanol melamine resin,
benzoguanamine resin and mixtures thereof.
6. A method for making color filters according to claim 4, wherein the
pigment is selected from the group consisting of azo lake organic
pigments, quinacridone organic pigments, phthalocyanine organic pigments,
isoindolinone organic pigments, anthraquinone organic pigments, thioindigo
organic pigments, chrome yellow, chrome blue, iron oxide, chrome
vermilion, chrome green, ultramarine, prussian blue, cobalt green, emerald
green, titanium white, carbon black, and mixtures thereof.
7. A method for making color filters according to claim 4, wherein the dye
is selected from the group consisting of azo dyes, anthraquinone dyes,
benzodifuranone dyes, condensed methine dyes, and mixtures thereof.
8. A method for making color filters according to claim 1, wherein when
three regions of different initial levels of exposure energy are formed on
the substrate, D.sub.1, D.sub.2 and D.sub.3 represent from 100% to 40%,
from 85% to 20% and from 70% to 0%, respectively.
9. A method for making color filters according to claim 8, wherein D.sub.1,
D.sub.2 and D.sub.3 represent from 100% to 70%, from 70% to 40% and from
40% to 0%, respectively.
10. A method for making color filters according to claim 1, wherein when
four regions of different initial levels of exposure energy are formed on
the substrate, D.sub.1, D.sub.2, D.sub.3 and D.sub.4 represent from 100%
to 40%, from 85% to 20%, from 70% to 5% and from 50% to 0%, respectively.
11. A method for making color filters according to claim 10, wherein when
four regions of different initial levels of exposure energy are formed on
the substrate, D.sub.1, D.sub.2, D.sub.3 and D.sub.4 represent from 100%
to 80%, from 80% to 50%, from 50% to 30% and from 30% to 0%, respectively.
12. A method for making color filters according to claim 1, wherein step
(a) comprises a single exposure step using a photomask having multiple
exposure density; or using a photomask having a predetermined exposure
pattern by careful movements of the photomask to form regions of different
degrees of exposure energy on the photoresist of the substrate; or using a
plurality of photomasks to form the desired three regions of different
degrees of initial exposure energy form regions of different degrees of
exposure energy on the photoresist of the substrate.
13. A method for making color filters according to claim 1, wherein the
developer solution of step (c) is selected from the group consisting of
the aqueous solutions of sodium carbonate, sodium hydrogen carbonate,
sodium silicate, tetraalkyl amine compounds, sodium hydroxide, potassium
hydroxide, and mixtures thereof.
14. A method for making color filters according to claim 1, wherein in step
(e) the substrate is selectively or progressively coated with the color
electrodeposition coating containing red, green and blue.
15. A method for making color filters according to claim 1, wherein when
three regions of different initial levels of exposure energy are formed on
the substrate, the substrate is pre-arranged with a black-hued matrix.
16. A method for making color filters according to claim 15, wherein the
materials of forming the black-hued matrix are alloys or oxides of
chromium and/or nickel, or mixtures thereof, or organic polymeric coating
compositions containing black pigments dispersed therein or
non-electrically conductive materials.
17. A method for making color filters according to claim 1, wherein when
four regions of different initial levels of exposure energy are formed on
the substrate, a black resin is coated onto the last region of the
substrate and steps (c) and (d) are repeated to complete the
electrodeposition of all colors.
18. A method for making color filters according to claim 1 further
comprising baking the substrate again after step (e) in order to cure the
electrodeposition resins of all colors completely.
Description
BACKGROUND OF THE INVENTION
Flat panel displays (FPD) are products in the photoelectric industry, which
combine the techniques of semiconductors, optics and chromatics. A trend
is becoming increasingly recognizable in that FPD is gradually taking the
place of the traditional cathode ray tubes (CRT). Among various flat panel
displays, liquid crystal displays (LCD) have assumed a leading position,
because of their light weight, thinness and capability of becoming a
full-color display. Color filters are the key elements to render
glistening and vivid pictures.
A color filter comprises three main components: a black-hued matrix, a
color filter layer and an overcoat. Currently, commercial methods for
manufacturing color filters include:
(1) dyeing,
(2) etching,
(3) pigment dispersion,
(4) electrodeposition, and
(5) printing.
The dyeing method and the etching method primarily utilize dyes as the
essential filtering materials. The advantages of using dyes as the
essential filtering materials lie in their variant species, homogeneous
chroma, high dyeability, high color intensity and high light
transmissibility. Suitable dyes are disclosed in U.S. Pat. Nos. 4,820,619
and 4,837,098. Because of the relatively inadequate light and heat
resistance of the dyeing materials, the methods of dyeing and etching have
been largely replaced by the pigment dispersion method and the
electrodeposition method that use pigments as the essential filtering
materials. Pigments have superior light and heat resistance. One simply
has to utilize a general pigment dispersion technique to control the
particle size of the pigment to be less than 0.1 .mu.m, these two methods
will enable pigments to perform color intensity and light transmissibility
close to or even the same as dyes perform. Due to the above, the pigment
dispersion method and the electrodeposition method have become the major
methods on which industries rely in the manufacture of color filters.
Pigment dispersion methods, such as those disclosed in U.S. Pat. Nos.
5,085,973 and 4,786,148 and Japan Laid-Open Patent Publication No.
60-129739, involve the use of a photosensitive resin well dispersed in
pigments and a photolithography technique to achieve a high resolution and
a flexibility of pattern design. This method is currently the major
manufacturing technique. However, due to the factors that (1) the efficacy
of the materials is low (1%.about.2%), (2) the trend of applying to large
sizes corresponding glass substrates is low and (3) the chances of using
an expensive precisely aligning machine are quite frequent, the cost of
production for such a method fails to comply with the trends of large
sizes of color liquid displays and of lower prices.
Electrodeposition coating processes, such as that disclosed in U.S. Pat.
No. 4,812,387, use an electrophoresis technique to electrodeposite an
electrodeposition resin and a pigment which are both well dispersed in
water onto a patterned transparent electrode substrate. A filter layer of
a uniform thickness and of a good smoothness is obtained. The
electrodeposition coating technique is limited in its applications. Owing
to the design of the electrodes, electrodeposition coating process can
only use a substrate with a stripe pattern of conductive film for
implementation. Thus, it is impossible to arrange pixels freely.
Among all the processes for manufacturing color filters, the printing
process is the least expensive process. However, it suffers from the
problems of poor dimensional precision, smoothness and reliability.
Printing processes are not well accepted by industries for making high
quality electronic products, but are generally used in the manufacture of
low-end products.
To address the problems and at the same time to preserve the advantages of
pigment dispersion and electrodeposition coating process, Nippon Oil
Company proposed an electrodeposition lithographic method (ED-litho) for
making color filters which combined the electrodeposition (ED) coating
method and the lithographic (litho) technique. As disclosed in U.S. Pat.
Nos. 5,214,541 and 5,214,542, the contents of which are incorporated
herein by reference, Nippon Oil Company discloses foremost an
electrodeposition lithographic method. Said method involves the steps of
exposing a photoresist layer on a transparent electrically conductive
layer under a photomask having patterns of more than three different
degrees of light transmittances for one time to form regions of different
degrees of exposure energy, using different developer solutions to remove
the photoresist layer stepwise and electrodepositing progressively the
red, green and blue colors onto the exposed electrically conductive
substrate. The electrodeposition lithographic method discussed above has
several advantages:
(1) The method combines the techniques of electrodeposition and
lithography. Therefore, high precision patterns can be obtained, better
than that obtainable from the electrodeposition coating method;
(2) The pattern figure has a high degree of freedom, and both stripe and
non-stripe patterns can be provided; and
(3) Because it utilizes the advantageous characteristics of an
electrodeposition process, the coated films exhibit uniform film thickness
and excellent smoothness.
However, the electrodeposition lithographic method requires developer
solutions of at least three different levels of concentrations so as to
selectively remove the exposed photoresist at different stages of the
development process and to electrodeposite the colors of red, green and
blue (R, G, B) thereunto, thus it allows only a relatively narrow process
window within which tolerance is acceptable. Moreover, it is known to use
basic aqueous developer solutions for positive photoresist. Under such
circumstances, there exist only very limited options in selecting an
appropriate electrodeposition resin. Additionally, there still exists
photoresist on the substrate before the electrodeposition of all desired
colors is accomplished. Thus, a culing (hardened) procedure at elevated
temperature is impossible. In the examples of this reference, a color
electrodeposition coating comprising an anionic electrodeposition resin is
used. The acid value of said resin is in the range of from 100 to 500 mg
KOH/g. Such type of anionic electrodeposition resin is easily influenced
by developer solutions. Therefore, developer solutions of higher
concentrations can not be applied. This results in a narrow tolerance of
developer solutions. Although cationic electrodeposition resins have
better basic resistance, they show the disadvantages of be easily yellowed
and having a lower transmission. During the electrodepositing process,
such type of resin tends to reduce the indium tin oxide (ITO), which is a
commonly used transparent electrically conductive material of the
transparent electrically conductive substrate, to black spots. The above
recited technical limits are believed to be the main reasons why there are
no commercialized products produced from the process.
Another method for making color filters which combined a electrodeposition
(ED) coating method and a lithographic (litho) technique is disclosed in
U.S. Pat. No. 5,641,595. The contents of said patent are incorporated
herein by reference. Said method is characterized by utilizing the energy
accumulate characteristic of positive photoresist in combination with
light-curable electrodeposition resins. Said process involves the steps of
coating a layer of positive photoresist onto a transparent electrically
conductive substrate and exposing the positive photoresist layer to form
regions of different initial levels of exposure energy. One of the regions
reaches the full exposure energy of the positive photoresist. After a
developing step, the photoresist on this region is removed and the
corresponding electrically conductive substrate is uncovered. Said region
is then electrodeposited to form the desired colors. When all steps of the
method are accomplished, the substrate is subjected to an exposing step
without alignment. The pixels electrodeposited previously are then cured
by light. This step can avoid the electrodeposited color from being
attacked by the developer solution used in the next stage. The regions
which have not accumulated sufficient amounts of energy are subject to
next exposure to ensure that the energy of the second region reaches the
full exposure energy of said positive photoresist. After that, each region
is developed with developer solution and electrodeposited with the desired
color. Repeat the above steps until the arrangement of all the pixels is
accomplished.
This energy incremental process possesses the function of developing the
regions of different levels of exposure energy progressively. Because the
method combines the advantages of using the photocurable anionic
electrodeposited resins, making up the exposure energy to allow each
region to reach the full exposure energy of the positive photoresist, and
curing the film formed by the electrodeposition coating, the influence of
the basic developer solution subsequently used on the electrodeposited
pixels is eliminated and the developing step is simplified. However, the
photocurable electrodeposited resins require a sufficient amount of
exposure energy to cure the electrodeposited coating so as to defend
against the attack of developer solutions. In order to possess a filtering
function, pigment particles are dispersed into the electrodeposited
coating. Thus, the energy need to expose the coating becomes even greater.
This narrows the exposure tolerance of the photoresist. Moreover, the
addition of photosensitive groups in the electrodeposited coating enhances
the difficulty to achieve well dispersion and stability, and adversely
influences the yield rate of the products.
The present invention intends to overcome the problems and to preserve the
advantages of pigment dispersion and electrodeposition coating process for
manufacturing color filters. The invention develops an excellent technique
for manufacturing color filters by using a color electrodeposition coating
containing an anionic electrodeposition resin having a low acid value in
combination with a weak basic developed positive photoresist. Since the
present invention utilizes an anionic electrodeposition resin having a low
acid value in combination with a weak basic developed positive photoresist
solution, the pixels of the corresponding regions electrodeposited
previously can be baked at a normal drying temperature so as to defend
against the attack of developer solutions used subsequently for developing
other desired colors of pixels without influencing the functions of the
photoresists. The method of the invention shows the advantages of having a
high degree of freedom in pattern figures and a wide process window.
Moreover, the manufacture color filters of large surface and a perfect
yield rate of products are possible.
SUMMARY OF THE INVENTION
The invention relates to a method for manufacturing color filters utilizing
a color electrodeposition coating which contains an anionic
electrodeposition resin having a low acid value. Said method comprises
coating a layer of positive photoresist onto a transparent electrically
conductive substrate, exposing the substrate under a photomask or
photomasks to form regions of different initial levels of exposure energy,
exposing the entire surface of the substrate through an
energy-incrementing way to, progressively, allow all regions of the
substrate to achieve an energy sufficient to completely expose the
photoresist on each corresponding region, developing stepwise each region
with a same developer solution to cause the electrically conductive
substrate of the corresponding region uncovered, electrodepositing said
region with a color electrodeposition coating containing an anionic
electrodeposition resin having an low acid value to finish the pixel
arrangements of the desired colors and completely exposing the substrate.
The low acid value anionic electrodeposition resin utilized in the
invention has an acid value of 1 to 70 mg KOH/g.
The method of the invention shows the advantages of having a high degree of
freedom in pattern figures and a wide process window. Moreover, the
manufacture color filters of large surface and the perfect yield rate of
products are possible.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1A(a) to 1A(f) is a schematic diagram showing the various stages of a
process for manufacturing color filters in accordance with the present
invention in which the transparent electrically conductive substrate has
been arranged with a black-hued matrix.
FIG. 1B(a) to 1B(f) is a schematic diagram showing the various stages of
another process for manufacturing color filters in accordance with the
present invention in which the transparent electrically conductive
substrate has been arranged with a black-hued matrix.
FIG. 2(a) to 2(f) is a schematic diagram showing the various stages of
another process for manufacturing color filters in accordance with the
present invention in which the transparent electrically conductive
substrate has not been arranged with a black-hued matrix.
DETAILED DESCRIPTION OF THE INVENTION
The invention relates to a method for manufacturing color filters
comprising the steps of:
(a) coating a layer of positive photoresist onto a transparent electrically
conductive substrate, and exposing the positive photoresist layer to form
three or four regions of different initial levels of exposure energy,
wherein the exposure energy of each region is D.sub.1, D.sub.2, D.sub.3
(and D.sub.4) progressively, D.sub.1 represents the full exposure energy
of the positive photoresist, and D.sub.1 >D.sub.2 >D.sub.3 (>D.sub.4);
(b) using a developer solution to develop and to remove the region of the
photoresist layer with the exposure energy of D.sub.1 to thereby cause a
corresponding area of the electrically conductive substrate underlying the
photoresist to be uncovered, and electrodepositing said region with a
color electrodeposition coating containing a low acid value anionic
electrodeposition resin having an acid value of lower than 70 mg KOH/g so
as to finish the pixel arrangement of a desired color;
(c) exposing the entire surface of the substrate with an energy IE.sub.n to
impart an incremental amount of energy to all regions of the substrate,
wherein IE.sub.n is the energetic difference between D.sub.n and D.sub.n+1
and the definition of n is below:
(i) when three regions of different initial levels of exposure energy are
formed on the substrate, n is 1 and 2 progressively, or
(ii) when four regions of different initial levels of exposure energy are
formed on the substrate, n is 1, 2 and 3 progressively;
(d) after each time of exposure in steps (c)(i) or (ii), using the same
developer solution of step (b) to develop and to remove the photoresist of
the region achieving full exposure to thereby cause the corresponding area
of the electrically conductive substrate of underlying the photoresist to
be uncovered, and then electrodepositing said region with a color
electrodeposition coating containing an anionic electrodeposition resin
having a low acid value to finish the pixel arrangements of other desired
colors;
(e) repeating steps (c) and (d) until all of the pixel arrangements are
accomplished; and
(f) forming an overcoat on the substrate.
The transparent electrically conductive substrate of the invention can be
selected from the group consisting of oxides of tin, indium and antimony,
such as indium tin oxide(ITO), and mixtures thereof; or a commercialized
electrically conductive glass.
The materials for forming the black-hued matrix can be alloys or oxides of
chromium, nickel, etc., or mixtures thereof. Alternatively, the black-hued
matrix can be formed from an organic polymeric coating composition
containing black pigments dispersed therein. For example, the materials
can be electrically conductive, such as acrylate resins and epoxy resins,
or non-electrically conductive.
The positive photoresist (PR) to be used in the invention can be selected
from the group consisting of novolak resins and naphthyoquinone diazide
compounds and the derivatives thereof. Suitable positive photoresists are
those disclosed in U.S. Pat. No. 5,645,970. The energy-accumulable
quantity of those materials allows the regions of different initial
exposure energy to be progressively developed. A positive photoresist
works based on the principle that its solubility increases after being
exposed to photoenergy, thus it becomes capable of being developed by a
basic solution. The precise reliability of patterns of photoresists is
high and the size accuracy is perfect. Preferably, the photoresist for use
in the process of the present invention should have high contrast so as to
minimize the film loss in the unexposed or underexposed areas.
The techniques for coating photoresists can be any that conventionally
known to persons skilled in the art such as spraying, dip coating, screen
printing, roll coating, spin coating. Preferably, the photoresist layer
has a thickness of 1 to 10 .mu.m, more preferably 1.5 to 5 .mu.m.
If the photoresist layer form three regions of different degrees of
exposure energy after exposing, the exposure energy of each region,
D.sub.1, D.sub.2 and D.sub.3 represents from 100% to 40%, from 85% to 20%
and from 70% to 0%, respectively. Preferably, each D.sub.1, D.sub.2 and
D.sub.3 represents from 100% to 70%, from 70% to 40% and from 40% to 0%,
respectively. If the photoresist layer form four regions of different
degrees of exposure energy after exposing, the exposure energy of each
region, D.sub.1, D.sub.2, D.sub.3 and D.sub.4, represents from 100% to
40%, from 85% to 20%, from 70% to 5% and from 50% to 0%, respectively.
Preferably, each D.sub.1, D.sub.2, D.sub.3 and D.sub.4, represents from
100% to 80%, from 80% to 50%, from 50% to 30% and from 30% to 0%,
respectively.
The energy of full exposure required in a photoresist manufacture is
between 80 and 1500 mJ/cm.sup.2. It can be done via a single exposure step
using a photomask having multiple exposure density. Alternatively, it can
be accomplished using a photomask having a predetermined exposure pattern.
By careful movements of the photomask, regions of different degrees of
exposure energy can be formed on the photoresist. Another alternative
procedure is to use a plurality (three or four) of photomasks to form the
desired three regions of different degrees of initial exposure energy
which can be sequentially developed using the incremental exposure method
disclosed in the present invention. The regional pattern can be stripe or
non-stripe (such as mosaic or triangle, etc.) freely arranged one.
A positive photoresist is typically developed by a basic developer
solution, such as the aqueous solutions of sodium carbonate, sodium
hydrogen carbonate, sodium silicate, tetraalkyl amine compounds, sodium
hydroxide, potassium hydroxide, and mixtures thereof. The concentration of
the developer solution generally ranges from 0.1 to 10 wt %, preferably
from 0.2 to 4 wt %. The developing temperature is generally from
10.degree. to 70.degree. C., preferably from 15.degree. to 40.degree. C.
The time needed for the developing step is typically from 5 to 600
seconds.
Crosslinkable curing agents, organic solvents, neutralization agents and a
coloring agent consisting of a dye, a pigment, or a mixture thereof can be
added into the color electrodeposition coating containing an anionic
electrodeposition resin having a low acid value used in the present
invention.
The low acid value anionic electrodeposition resin used in the present
invention is preferably a polyester resin having carboxyl groups. The
resin can be dissolved or dispersed in a neutralization agent. Preferably,
said resin has an acid value of lower than 70 mg KOH/g, preferably from 20
to 70 mg KOH/g, and a solid content of about 75%. The monomers consisting
of the polyester resin may comprise those selected from the group
consisting of neopentyl glycol, adipic acid, isophthalic acid, isodecanol,
trimellitic anhydrate, butyl cellosolve and 2-butanol.
The neutralization agent can be selected from the group consisting of
dimethyl ethanol amine, diethyl ethanolamine, diisopropanolamine,
triethylamine and the mixtures thereof. Crosslinkable curing agents
suitably for use in the invention can be selected from the group
consisting of methylation melamine resin, butylation melamine resin,
methylation methanol melamine resin, butylation methanol melamine resin,
benzoguanamine resin.
The coloring agent of the present invention can be a dye, a pigment, or a
mixture thereof. Typically, an appropriate dye can be selected from the
group consisting of azo dyes, anthraquinone dyes, benzodifuranone dyes,
condensed methine dyes, and mixtures thereof. The pigment can be selected
from the group consisting of azo lake organic pigments, quinacridone
organic pigments, phthalocyanine organic pigments, isoindolinone organic
pigments, anthraquinone organic pigments, thioindigo organic pigments,
chrome yellow, chrome blue, iron oxide, chrome vermilion, chrome green,
ultramarine, Prussian blue, cobalt green, emerald green, titanium white,
carbon black, and mixtures thereof.
According to the process of the present invention, when three regions of
different degrees of exposure energy are formed on the substrate, the
substrate is pre-arranged with black-hued matrixes, and selectively or
progressively coated with the color electrodeposition coating containing
red, green and blue. When four regions of different degrees of exposure
energy are formed on the substrate, a black resin is electrodeposited onto
the last region (the fourth region) after the color electrodeposition
coating containing red, green and blue be selectively or progressively
electrodeposited. The developing and full-exposing steps can be repeated
until all of the pixels arrangements are accomplished. When all of the
pixels arrangements are accomplished in accordance with the invention, the
substrate is preferably baked to allow the electrodeposition resin to be
cured completely.
Anionic electrodeposition resins show excellent storage stability (the
property of not turning yellow), emulsification stability and pigments
disperibility (in particularly the pigments disperibility at high
concentration). When anionic electrodeposition resin is used in
combination with photoresist, there still exists the photoresist on the
substrate before the electrodeposition of all desired colors is
accomplished. There is no way to conduct a thermal-curing procedure at
elevated temperature. For anionic electrodeposition resin, the possibility
of being attacked by developer solutions used subsequently still exists.
To avoid such a disadvantage, the invention uses a color electrodeposition
coating containing an anionic electrodeposition resin having an acid value
of lower than 70 mg KOH/g in combination with a weak basic developed
positive photoresist solution. The method of the invention utilizes an
energy incremental way and develops the photoresist stepwise with
developer solution of one single concentration. After the corresponding
region of the electrically conductive substrate is uncovered, the region
is electrodeposited with a color to arrange the pixel. In a word, the
present invention is characterized by using an electrodeposition coating
containing an anionic electrodeposition resin having an acid value of
lower than 70 mg KOH/g in combination with a positive photoresist
technique possessing an energy incremental function. For example, the weak
basic developed positive photoresist solution disclosed in U.S. Pat. No.
5,645,970 can be used. Therefore, the pixels of the corresponding regions
electrodeposited previously can be baked at a normal drying temperature
such as from 80 to 120.degree. C. so as to defend the attack of developer
solutions used subsequently for developing other desired colors of pixels
without influencing the functions of the photoresists.
The method of the invention shows the advantages of having a high degree of
freedom in pattern figures and a wide process window. Moreover, the
manufacture color filters of large surface and the perfect yield rate of
products are possible.
Each of FIGS. 1A and 1B represents a preferred embodiment in accordance
with the present invention. Both of the two embodiments are directed to a
method for making color filters in which the transparent electrically
conductive substrate has been arranged with a black-hued matrix. Said
method comprises the following steps:
1. pre-forming, a black-hued matrix on a transparent electrically
conductive substrate (2); said black-hued matrix can be made from a
conductive material or a non-conductive material as shown in (3) of FIG.
1A(a) and (13) of FIG. 1B(a) respectively;
2. coating a layer of positive photoresist onto a transparent electrically
conductive substrate (2) and exposing the photoresist layer under a
photomask or photomasks to form three regions of different initial levels
of exposure energy, wherein the exposure energy of each region is D.sub.1
(5), D.sub.2 (6) and D.sub.3 (7) respectively, wherein D.sub.1 represents
the full exposure energy of the positive photoresist and D.sub.1 >D.sub.2
>D.sub.3, as shown in FIG. 1A(a) and FIG. 1B(a);
3. using a developer solution to develop and to remove the region of the
photoresist layer with the exposure energy of D.sub.1 (5) to thereby cause
a corresponding area of the electrically conductive substrate underlying
the photoresist to be uncovered, and electrodepositing said region with a
color electrodeposition coating containing an anionic electrodeposition
resin having a low acid value, namely, conducting the electrodepositing
arrangement of the first pixel (8), as shown in FIG. 1A(b) and FIG. 1B(b);
4. exposing the entire surface of the substrate with an energy IE.sub.1 to
impart an incremental amount of energy to all regions of the substrate,
wherein IE.sub.1 is the energetic difference between D.sub.1 and D.sub.2
in other words, IE.sub.1 =D.sub.1 -D.sub.2), at this moment, the exposure
energy of the region whose initial exposure energy is D.sub.2 (6) has been
accumulated to the amount of full exposure (D.sub.2 +IE.sub.1
=D.sub.1)(6'), and the exposure energy of the region whose initial
exposure energy is D.sub.3 (7) has not been accumulated to the amount of
full exposure (only D.sub.3 +IE.sub.1)(7'), as shown in FIG. 1A(b) and
FIG. 1B(b);
5. using the same developer solution as that of step 3 to develop and to
remove the photoresist of the region achieving full exposure (6') to
thereby cause the corresponding area of the electrically conductive
substrate underlying the photoresist to be uncovered, and
electrodepositing said region with a color electrodeposition coating
containing an anionic electrodeposition resin having a low acid value,
namely, conducting the electrodepositing arrangement of the second pixel
(9, 19), as shown in FIG. 1A(c)/(d) and FIG. 1B(c)/(d);
6. exposing the entire surface of the substrate with an energy IE.sub.2 to
impart an incremental amount of energy to all regions of the substrate,
wherein IE.sub.2 is the energetic difference between D.sub.2 and D.sub.3
in other words, IE.sub.2 =D.sub.2 -D.sub.3), at this moment, the exposure
energy of the region whose initial exposure energy is D.sub.3 (7) has been
accumulated to the amount of full exposure (D.sub.3 +IE.sub.1 +IE.sub.2
=D.sub.1)(7"), as shown in FIG. 1A(c)/(d)and FIG. 1B(c)/(d);
7. using the same developer solution as that of step 3 to develop and to
remove the photoresist of the region achieving full exposure (7") to
thereby cause the corresponding area of the electrically conductive
substrate underlying the photoresist to be uncovered and electrodepositing
said region with a color electrodeposition coating containing an anionic
electrodeposition resin having a low acid value, namely, conducting the
electrodepositing arrangement of the third pixel (10, 20) and baking the
substrate at an elevated temperature to allow the pixels (figures) to be
cured completely, as shown in FIG. 1A(e) and FIG. 1B(e);
8. finally, forming an overcoat (11, 21) on the substrate to protect the
colored filter, as shown in FIG. 1A(f) and FIG. 1B(f).
FIG. 2 is a schematic diagram showing the various stages of another process
for manufacturing color filters in accordance with the present invention
in which the transparent electrically conductive substrate is not been
arranged with a black-hued matrix. Said method comprises the following
steps:
1. coating a layer of positive photoresist onto a transparent electrically
conductive substrate (2) and exposing the photoresist layer under a
photomask or photomasks to form four regions of different initial levels
of exposure energy, wherein the exposure energy of each region is D.sub.1
(22), D.sub.2 (23), D.sub.3 (24) and D.sub.4 (25) respectively, wherein
D.sub.1 represents the full exposure energy of the positive photoresist
and D.sub.1 >D.sub.2 >D.sub.3 >D.sub.4, as shown in FIG. 2(a);
2. using a developer solution to develop and to remove the region of the
photoresist layer with the exposure energy of D.sub.1 (22) to thereby
cause a corresponding area of the electrically conductive substrate
underlying the photoresist to be uncovered, and electrodepositing said
region with a color electrodeposition coating containing an anionic
electrodeposition resin having a low acid value, namely, conducting the
electrodepositing arrangement of the first pixel (26), as shown in FIG.
2(b);
3. exposing the entire surface of the substrate with an energy IE.sub.1 to
impart an incremental amount of energy to all regions of the substrate,
wherein IE.sub.1 is the energetic difference between D.sub.1 and D.sub.2
namely, IE.sub.1 =D.sub.1 -D.sub.2), at this moment, the exposure energy
of the region whose initial exposure energy is D.sub.2 (23) has been
accumulated to the amount of full exposure (D.sub.2 +IE.sub.1
=D.sub.1)(23'), and the exposure energies of the regions whose initial
exposure energy is D.sub.3 (24) and D.sub.4 (25) respectively have not
been accumulated to the amount of full exposure [only (D.sub.3
+IE.sub.1)(24') and (D.sub.4 +IE.sub.1)(25') respectively], as shown in
FIG. 2(b);
4. using the same developer solution as that of step 3 to develop and to
remove the photoresist of the region achieving full exposure (23') to
thereby cause the corresponding area of the electrically conductive
substrate of underlying the photoresist to be uncovered, and
electrodepositing said region with a color electrodeposition coating
containing an anionic electrodeposition resin having a low acid value,
namely, conducting the electrodepositing arrangement of the second pixel
(27), as shown in FIG. 2(c)/(d);
5. exposing the entire surface of the substrate with an energy IE.sub.2 to
impart an incremental amount of energy to all regions of the substrate,
wherein IE.sub.2 is the energetic difference between D.sub.2 and D.sub.3
namely IE.sub.2 =D.sub.2 -D.sub.3), at this moment, the exposure energy of
the region whose initial exposure energy is D.sub.3 (24) has been
accumulated to the amount of full exposure (D.sub.3 +IE.sub.1 +IE.sub.2
=D.sub.1)(24"), however, the exposure energy of the region whose initial
exposure energy is D.sub.4 (25) has not been accumulated to the amount of
full exposure (only D.sub.4 +IE.sub.1 +IE.sub.2)(25"), as shown in FIG.
2(c)/(d);
6. using the same developer solution as that of step 3 to develop and to
remove the photoresist of the region achieving full exposure (24") to
thereby cause the corresponding area of the electrically conductive
substrate of underlying the photoresist to be uncovered and
electrodepositing said region with a color electrodeposition coating
containing an anionic electrodeposition resin having a low acid value,
namely, conducting the electrodepositing arrangement of the third pixel
(28), as shown in FIG. 2(c)/(d);
7. exposing the entire surface of the substrate with an energy IE.sub.3 to
impart an incremental amount of energy to all regions of the substrate,
wherein IE.sub.3 is the energetic difference between D.sub.3 namely,
IE.sub.3 =D.sub.3 -D.sub.4), and D.sub.4, at this moment, the exposure
energy of the region whose initial exposure energy is D.sub.4 (25) has
been accumulated to the amount of full exposure (D.sub.4 +IE.sub.1
+IE.sub.2 +IE.sub.3 =D.sub.1)(25'"), and then using the same developer
solution as that of step 3 to develop and to remove the photoresist of the
region achieving full exposure (25'") to thereby cause the corresponding
area of the electrically conductive substrate of underlying the
photoresist to be uncovered, and coating said region with a layer of black
resin, shining a UV light onto the back side of said conductive substrate
so as to cure the black-hued matrix (29) filled in holes of the region
under a shielding effect provided by said cured resins (26, 27, 28); the
kinds of the materials forming the black-hued matrix and the ways to
produce the same can comprise the following three: (1) employing a
heat-curable positive photoresist dispersed with black coloring agents and
using the region which has the less initial exposure energy to form
black-hued matrix thereon, (2) employing a black electrodeposition resin
which is of the same type as that contained in the electrodeposition
coating and utilizing an electrodepositing method to arrange the black
electrodeposition resin on a electrically conductive substrate, (3)
employing a photosensitive black electrodeposition resin and baking the
substrate at elevated temperature to cure the pixels (26, 27, 28) and the
black-hued matrix (29) completely, as shown in FIG. 2(e);
8. finally, forming an overcoat (30) on the substrate to protect the
colored filter, as shown in FIG. 1A(f) and FIG. 2(f).
The examples of the present invention are described below. It is believed
that the other purposes, characteristics and advantages of the present
invention can be more definitely understood through the illustration of
the examples.
EXAMPLES
Example 1
Synthesis of Polyester Resin Having a Low Acid Value
Using a conventionally known esterifying condensation polymerization to
carry out the synthesis of a polyester resin of low acid value. The
species and amounts of the monomers and solvents used are as below:
______________________________________
Components Amount, wt %
______________________________________
neopentyl glycol
24.53
adipic acid 3.25
isophthalic acid
7.95
isodecanol 14.40
trimellitic anhydrate
25.81
buytyl cellosolve
5.00
2-butanol 20.00
______________________________________
Place the chemical reagents as indicated above into a reactor. Stir the
mixture under a nitrogen atmosphere at elevated temperature to carry out
the reaction. After esterification and dewatering under reduced pressure,
the polymerization is finished. The analytical results of the resin
solution obtained are below:
______________________________________
non-volatile components (150.degree. C. 1 hr. wt %)
75.4
low acid value (mg KOH/g, solid)
48.7
viscosity (25.degree. C., cps)
45.2
______________________________________
Example 2
Production of the Electrodeposition Coating Containing Polyester Resin
Having a Low Acid Value
The species and amounts of the components of the electrodeposition coating
containing a polyester resin of low acid value are as below:
______________________________________
Components A-1 A-2 A-3
______________________________________
anionic polyester resin
95.0 95.0 95.0
melamine resin Nikarakku .RTM. MX-40)
8.0
8.0
8.0
2-ethoxy ethanol butyl ether
25.0
25.0
2-ethoxy ethanol ethyl ether
5.0
5.0
neobutanol 18.0 18.0
18.0
triethylamine 2.5, 2.5
2.5
deionized water 813.5 813.5
813.5
phthalocyanine blue (SR-1500)
--
--
phthalocyanine green (SAX)
5.0
--
azo lake pigment (CARMINE FB)
-- -- 5.0
total 1000 1000 1000
______________________________________
Use the following steps to prepare the electrodeposition coating containing
polyester resin having a low acid value:
1) weight the anionic polyester resin, melamine resin (Nikarakku.RTM.
MX-40), 2-ethoxy ethanol butyl ether, 2-ethoxy ethanol ethyl ether,
neobutanol and triethylamine with the amounts shown in the above, place
the reagents into a container, and mix them under stirring;
2) weight the pigments with the amounts shown in the above, add them into
the mixture, and mix them under stirring;
3) milling-disperse the mixture with a mill, the milling beads used have an
average particle size of from 0.8 to 1.2 .mu.m;
4) add deionized water under stirring and emulsify the mixture; and
5) filter the mixture with a filter of 5 .mu.m.
Example 3
A positive photoresist of 2.2 .mu.m thick and corresponding to a weak basic
developer solution as disclosed in U.S. Pat. No. 5,645,970 was formed on
an electrically conductive transparent glass substrate, which was measured
0.7 mm in thickness and contains a pre-arranged black-hued matrix. A
photomask with merely one-third light-transmitting area was used by
carefully moving to conduct the energy exposure of 250, 150 and 50
mJ/cm.sup.2 respectively (100%, 60% and 20%) to form three regions of
different initial exposure energies.
A developer solution containing 0.5% Na.sub.2 SiO.sub.3 was used to develop
and to remove the 250 mJ/cm.sup.2 initial exposure region (i.e., 100%
initial exposure region). Therefore, a resin containing a red pigment was
electrodeposited onto the expose surface of the conductive substrate. The
electrodeposition process was conducted at 25.degree. C. at an electrical
voltage of 50 V, for 20 seconds. After the electrodeposition process was
accomplished, the substrate was washed with deionized water and the
substrate was dried at 90.degree. C. for 10 minute. The entire photoresist
was then exposed to a light source to receive 100 mJ/cm.sup.2 incremental
exposure energy. This caused the cumulative exposure energy in the second
(initially 100 mJ/cm.sup.2, or 60% initial exposure energy) and third
(initially 50 mJ/cm.sup.2, or 20% initial exposure energy) to raise to 250
mJ/cm.sup.2 (full exposure) and 150 mJ/cm.sup.2 (60% of full exposure),
respectively. Similarly, the same developer solution containing 0.5%
Na.sub.2 SiO.sub.3 was then used to develop and to remove the full
exposure region. This was followed by electrodepositing under a similar
condition a resin containing a green pigment onto the expose surface of
the conductive substrate and which was then dried it. Again, the entire
photoresist was exposed to a light source to receive another 100
mJ/cm.sup.2 of incremental exposure energy. This caused the cumulative
exposure energy in the third to raise to 250 mJ/cm.sup.2 (100% exposure).
The region was developed and removed using the same developer solution
containing 0.5% Na.sub.2 SiO.sub.3. This was again followed by
electrodepositing under a similar condition a resin containing a blue
pigment onto the expose surface of the conductive substrate. Finally, the
entire photoresist was exposed to receive another 100 mJ/cm.sup.2 of
exposure energy then removed using the same developing solution containing
0.5% Na.sub.2 SiO.sub.3. To ensure complete curing of all the colored
layers, the whole plate was heated at 260.degree. C. for one hour. The
arrangement of the three pixels, red, green and blue is finished.
The foregoing description of the preferred embodiments of this invention
has been presented for purposes of illustrated and description. Obvious
modifications or variations are possible in light of the above teaching.
The embodiments were chosen and described to provide the best illustration
of the principles of this invention and its practical application to
thereby enable those skilled in the art to utilize the invention in
various embodiments and with various modifications as are suited to the
particular use contemplated. All such modifications and variations are
within the scope of the present invention as determined by the appended
claims when interpreted in accordance with the breadth to which they are
fairy, legally, and equitably entitled.
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